The invention relates generally to seals for packages. More specifically, the invention relates to peelable seals needed for packages of perishable goods such as coffee.
A peelable seel is the seal or joint between two films produced by heat sealing or impulse sealing, the joint thus formed having the property of being able to open in the original plane of joining of the two films by the action of a pulling force, without wrenching off or tearing occurring in the material of the two films used to make up the joint. For purposes of the present invention, the peelable seal must possess a mechanical resistance sufficient to maintain the wholeness and the tight-seal properties of the packing and wrapping during storage and transport until such time as the packing or wrapping is opened by the user of the article. The mechanical resistance of the peelable seal must be low enough to permit ready manual opening of the joint, i.e., without the use of any auxiliary instrument.
In recent years, packaging machine designs have evolved such that more stress is placed on the just formed, still hot seals, thus requiring the packaging material to have higher hot tack performance to maintain seal hermeticity. In addition, packaging machine speeds have increased which in turn sacrifices time allowed to form a seal, resulting in the need to decrease the temperature required to form a seal. Further, many of these machines require precise control of the coefficient of friction of the sealant to provide a consistent drag over stationary machine components. Still further, it is desirable to form a strong heat seal of a degassing valve to the peel seal material.
The prior art discloses various blends of polymers used to form peel seals. These blends only partially provide the full range of properties necessary for a peel seal package, for example for coffee, in accordance with the objects of the present invention. For example, U.S. Pat. No. 4,252,846 (Romesberg) discloses a blend of ethylene vinyl acetate (EVA) copolymer and high density polyethylene (HDPE). While this blend may peel, the hot tack properties are not addressed and are therefore likely to be poor. Here, the peel seal is taught that has a wide sealing temperature range with minimum variance in the seal value from a selected peel strength. Here, the range is approximately plus or minus ten degrees Fahrenheit from the a control sealing temperature.
U.S. Pat. No. 4,665,130 (Hwo) discloses a film made from a blend of polypropylene, polyethylene and polybutylene. Here, the desired product has increased optical clarity such as low percent haze, for use with foodstuffs or medical products wrapped in transparent films. While this blend may peel, the hot tack properties again are not addressed and likely to be poor.
U.S. Pat. No. 4,666,778 (Hwo) discloses a film made from a blend of polypropylene, polyethylene and polybutylene. Again, a primary goal of this invention is to make a seal which exhibits good optical qualities, such as low percent haze, required, for example, for foodstuffs. While this blend may peel, the hot tack properties again are not addressed and likely to be poor.
U.S. Pat. No. 4,759,984 and 4,808,662 (both Hwo) disclose extrusion coating of polycarbonate or nylon film with a blend of polybutylene, ethylene vinyl acetate and polypropylene to form a peel seal. Here, the primary goal of these inventions is to avoid delamination layers when the sealed layers are pulled apart and utilizes a tie adhesive to bind incompatible substrates with sealants without the need for additional equipment to bind the adhesive between the sealant and the substrate. While this blend may peel, the hot tack properties are not specifically addressed and therefore are likely to be poor.
U.S. Pat. No. 4,810,541 (Newman) discloses a peel seal blend of polybutylene, ethylene vinyl acetate and polyethylene for producing the flange of a plastic container to which a lid is peelably sealed. The invention is in the area of rigid packages and is not applicable to this invention.
U.S. Pat. No. 4,859,514 (Friedrich) discloses a blend of EVA/EBC/PP designed to seal and peel from an ionomer or ionomer/EVA blend. This invention is not applicable since the subject invention is not designed to seal and peel to/from itself.
U.S. Pat. No. 4,870,134 (Hwo) discloses a blend of ethylene-carboxylic copolymer, butene-1, and polypropylene for forming easy opening packages. This blend may pose problems with consistent coefficient of friction since ethylene-carboxylic copolymer more readily absorbs compounds such as oleamide or erucamide. Furthermore, there is no disclosure regarding the hot tack properties of the blend.
U.S. Pat. No. 4,876,156 (Hwo) discloses a blend using a higher percentage of butene-1 than polyethylene and is therefore not applicable. Here, the important aspect of this invention is to provide a wrapping or packing material having easy peelability at the seal and yet which will bond to polypropylene without the aid of an adhesive and which are retortable at a temperature of 250 degrees Fahrenheit or above.
U.S. Pat. No. 4,882,229 (Hwo) discloses a blend of high molecular weight polybutylene and polyethylene to form a peel seal which has clean peel properties and is therefore not applicable. The product here is peelable at the seal and bonds to polypropylene without the aid of an adhesive, and will bond to other substrates using a tie layer adhesive having a clean sealing surface with few xe2x80x9cangel hairsxe2x80x9d contained therein upon opening of a sealed area.
U.S. Pat. No. 4,916,190 (Hwo) discloses a blend of polyethylene, polypropylene and polybutylene for retortable peel seal packaging and is therefore not applicable. Again, this wrapping or packing material has easy peelability at the seal and yet which will bond to polypropylene without the aid of an adhesive and which is retortable at temperatures of 250 degrees Fahrenheit or above.
U.S. Pat. No. 5,036,140 (Hwo) discloses a peel seal blend of polyethylene, polypropylene and polybutylene for extrusion lamination to polypropylene without adhesive. Again, this is not applicable to the subject invention. Here, the wrapping or packing material has easy peelability at the seal and bonds to polypropylene without the aid of an adhesive.
U.S. Pat. No. 5,066,543 (Hwo) discloses a peel seal blend with improved hot tack. The blend of EAA, polybutylene and polyethylene will indeed provide good hot tack. It has been our experience that these blends do not provide consistent peel seal strength and consistent slip properties.
U.S. Pat. No. 5,084,360 (Young) discloses a blend of polypropylene and two different butylene/ethylene copolymers to form a peel seal layer on oriented polypropylene. The application is in flexible packaging in the general field of snacks and confection. The blend is designed for peel seal, higher hot tack, and adhesion to polypropylene. The blend will likely have very poor adhesion to polyethylene and EVA copolymers since these two materials are lacking in this blend. Therefore, degassing valve seal strength will be poor.
U.S. Pat. No. 5,087,667 (Hwo) discloses a peel seal blend of polyethylene, polypropylene and polybutylene designed to bond to polypropylene without adhesive. Again, this is not applicable to the subject invention. Here, again, a wrapping or packing material has easy peelability at the seal and yet bonds to polypropylene without the aid of an adhesive.
U.S. Pat. No. 5,128,414 (Hwo) discloses a peel seal blend of polyethylene, polypropylene and polybutylene designed to bond to polypropylene without adhesive. Again this is not applicable to the subject invention. Here, again, a wrapping or packing material has easy peelability at the seal and yet bonds to polypropylene without the aid of an adhesive.
U.S. Pat. No. 5,302,442 (O""Brien) discloses a peel seal blend of polyethylene, polypropylene and polybutylene designed for co-extrusion with polypropylene and subsequent orientation. Again, this is not applicable to the subject invention.
U.S. Pat. No. 5,547,752 (Yanidis) discloses a peel seal blend of polybutylene and ionomer. This blend will likely have unacceptable coefficient of friction properties and, for example, will not likely seal to a degassing valve.
The prior art discloses various blends of polymers to form peel seals. These blends only partially provide the full range of properties necessary for a peel seal package for, for example, coffee. This invention provides all of the properties-higher hot tack, consistent peel seal to itself, lower seal initiation temperature, consistent coefficient of friction, low residual odor, and strong coffee valve seal.
It is a general object of this invention to provide a peel seal blend which addresses the needs of the prior art.
It is a further object of this invention to provide a peel seal blend having a high hot tack.
It is still a further object of this invention to provide a peel seal blend having consistent peel seal to itself.
It is yet a further object of this invention to provide a peel seal blend having a low seal initiation temperature.
It is a further object of this invention to provide a peel seal blend having a consistent coefficient of friction to provide consistent drag over stationary machine components.
It is still a further object of this invention to provide a peel seal blend having low residual odor.
It is yet a further object of this invention to provide a peel seal blend that provides for decreased time in forming a seal during manufacturing such that allowance is made for increased packaging machine speeds.
Finally, it is a further object of this invention to provide a peel seal blend providing for a strong coffee valve seal.
A blend of 1-polybutylene, m-LLDPE (linear low density polyethylene) and LDPE (low density polyethylene) was developed to produce film and laminate able to form a package with hermetic peelable seals with high hot tack strength and low seal initiation temperature. Hermetic peelable seals are needed for packages of perishable goods such as coffee. Seal hermeticity is required to prevent the ingress of oxygen or other deleterious compounds into the package through the seals. Prelability of the seal is desired for ready access to the product through hand manipulation of the seal.
A packaging film or sheet which is capable of forming peel seals having acceptable seal strengths, is disclosed which includes a polymer mixture consisting of a blend having proportionate amounts of from about 60 percent by weight to about 70 percent by weight of LDPE; from about 15 percent by weight to about 25 percent by weight of mLLDPE; and from about 10 percent by weight to about 20 percent by weight of 1-polybutylene.
The blend may form the inside sealant layer of a multi-layer flexible co-extruded film which includes the inside sealant layer and at least one additional laminar layer.
The substrate layer adjacent the inside sealant layer may be a polyethylene layer of, for example, LDPE, LLDPE, HDPE, or anhydride modified LLDPE.
The substrate layer adjacent the inside sealant layer may also be an olefin based material layer of, for example, an EVA copolymer, mLLDPE or MDPE.
The inside sealant layer is preferably less than about 0.001 inches thick and most preferably about 0.0003 inches thick.
The blend may include 1000 to 10,000 ppm of diatomaceous earth or silica to add microscopic roughness to aid in processing.
The blend may also include approximately 100 to 2000 ppm of fatty amides to modify the coefficient of friction of the blend also to aid in processing.